The number of items consuming electricity in modern vehicles, as well as their power consumption, is steadily rising. For this reason, it has been contemplated to equip vehicles with a 48V wiring system capable of supplying different electrical equipment (loads) in the vehicle with greater power at a constant amperage. Using 48V, however, creates a problem if an accidental short-circuit occurs, as stable arcs may develop, because 48V exceeds the arc ignition voltage.
Conventionally, electric lines are protected by fuses. However, since an arc represents an additional resistance in the line, the short-circuit current is limited such that the fuse may not be triggered.
Generally, a distinction is made between two types of arcs, i.e., serial and parallel arcs, which will be explained in more detail below.
FIG. 1 shows an example of a parallel arc, and particularly a circuit configuration with a 48V power source, as well as an amperage waveform over time. Parallel arcs appear parallel to the load. These are caused, e.g., by defective cable insulation, causing a short-circuit to occur toward the auto body or the existing 12V electric wiring system. With a parallel arc, the current has a series of spikes of several hundred amperes. However, since the spikes may be short-lived, an average current is often not enough to blow a fuse.
FIG. 2 shows an example of a serial arc, and particularly a circuit configuration with a 48V power source, as well as an amperage waveform over time. Serial arcs occur in series toward the load. They are caused, e.g., by a broken cable or damaged plug connections. Serial arcs act like an additional resistance in the electric circuit, thereby reducing the amperage relative to the intact state of the electric circuit. A serial arc therefore limits the load current, such that a fuse will not blow.
Both serial and parallel arcs produce very high temperatures, whereby a stable arc may greatly damage the vehicle. It is therefore desirable that a developing arc be detected at an early stage. It is, however, very difficult to tell the difference between a power limitation caused by a serial arc and fluctuations in the power consumption caused by the load.
Some conventional methods for the detection of arcs are known. Since an arc generates frequency components in the kilohertz range, attempts were made to detect the arc by evaluating the amperage- or voltage-frequency range (e.g., using a fast Fourier transform). Such a method is described, e.g., in EP 2040348 A2. However, depending on the load, it remains difficult to distinguish clearly between normal signal components and signal components caused by arcs. Moreover, such a method requires complex and expensive hardware comprising a signal processor. Optical arc detection, in which an arc is detected by an optical fiber surrounding a cable, represents another known method (see, e.g., DE 10 2004 051 734 A1). All these methods, however, have the disadvantage of relatively complex implementation and/or unreliable detection of the arc.